Find all the points of discontinuity of the greatest integer fun

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10. Find all the points of discontinuity of the greatest integer function defined by f(x) = [x], where [x] denotes the greatest integer less than or equal to x.


Let f(x) = [ x ]. Df = R
Let a be any real number ∈ Df.
Two cases arise:
Case I. If a is not an integer, then
Lt with straight x rightwards arrow straight a below space straight f left parenthesis straight x right parenthesis equals space Lt with straight x rightwards arrow straight a below space left square bracket straight x right square bracket equals left square bracket straight a right square bracket equals straight f left parenthesis straight a right parenthesis
⇒ f is continuous at x = a

Case II. If a ∈ 1, then f(a) = [ a ] = a and
Lt with straight x rightwards arrow straight a to the power of minus below space straight f left parenthesis straight x right parenthesis equals space Lt with straight x rightwards arrow straight a to the power of minus below left square bracket straight x right square bracket equals straight a minus 1
Lt with straight x rightwards arrow straight a to the power of plus below straight f left parenthesis straight x right parenthesis equals Lt with straight x rightwards arrow straight a to the power of plus below space left square bracket straight x right square bracket equals straight a
therefore Lt with straight x rightwards arrow straight a to the power of minus below straight f left parenthesis straight x right parenthesis space not equal to Lt with straight x rightwards arrow straight a to the power of plus below space straight f left parenthesis straight x right parenthesis
∴ f is not continuous at x = a, a ∈ I.
∴ function is discontinuous at every integral point.

 

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